Ball bearings are in wide use in industry, and are used among other places in various processing equipment, including for example mixing devices. Ball bearings used in mixing devices are in many ways similar to other ball bearing arrangements, and for example typically have an inner ring having an outward-facing groove or race, an outer ring having an inward-facing groove or race, as well as a number of spherical ball elements which are trapped within the space between the two races to provide rolling contact.
It is often desirable for the balls to be evenly or at least relatively evenly spaced at circumferential angles around the circle defined by the races. In order to accomplish such even circumferential spacing, an item known as a bearing retainer is often used. The bearing retainer is generally some form of ring shaped device that sits freely in the space between the two races and has some features that interact with the balls in order to hold them in the proper position.
Also, the balls typically are sized such that during the assembly process if they were all in contact with each other, the balls would take up half or less than half of the circumferential space between the races. That is because during assembly of the bearing, typically the balls are placed in the lower half of the outer race leaving room for the inner race to be inserted, and then the balls are moved into a more evenly dispersed configuration at which point the inner ring is physically trapped in place so that it can rotate with respect to the outer ring but is otherwise axially located. In such an installation method, it has been common to have a bearing retainer that is simply inserted from one side of the bearing and has projections that project in between the balls and thus function to space the balls apart.
The above described type of bearing is in wide use in industry and has found applications in process equipment including, for example, mixing devices. In some types of mixing devices, the entire bearing assembly is typically packed with grease or some other lubricating material. The grease sits within the space between the rings and sits on the balls to some extent, and provides lubrication, particularly for the rolling contact along the races and also for the sliding contact that occurs between surfaces of the retainer and the balls themselves.
A relatively new type of application for ball bearing assemblies has arisen in the case of process equipment and mixing devices that have a clean-in-place feature. In these clean-in-place type devices, which are particularly popular, for example, in the biotechnology and other industries requiring highly sterile cleanable equipment, the various surfaces of the bearing itself are exposed to the material that is being processed. For example, in a biotechnology mixing device, the bearings may be exposed to the fluid that is being mixed or otherwise treated. This is referred to sometimes as a dry running situation. This can have some advantages, in that the fluid being mixed often has lubricating properties of its own, and therefore it provides to some extent the lubrication that would have otherwise been provided by the grease. Another attribute of some of these clean-in-place devices, is that between operation cycles, the device is cleaned with a cleaning and/or flushing fluid. The cleaning and/or flushing fluid, during this cycle, also comes into contact with the bearing surfaces and in such a way removes and rinses away the material that was being processed in the prior cycle. It is desirable that this clean-in-place process does an effective job of removing or flushing away the materials from the prior cycle, and also that when the cleaning or flushing material is drained or removed, that as little residue, if any, as possible be left behind on the bearing so that it does not contaminate the material in the next cycle.
The prior art bearings described above were developed for use in a grease lubricated (i.e. not dry running) type situation. It has been found that these bearings may not perform optimally in the context of a dry running and/or a clean-in-place application at least to some extent for several reasons. The lubricating properties of the material being mixed may not be as good as was present with the grease, and it has been found that some prior art bearing retainers may tend to jam under load due to the heavy friction. Further, since the above-described prior art retainers tend to engage the balls only from one side, the jamming effect can urge the retainer to the side where it eventually further wedges into a jammed position. Also, during the clean-in-place process, the prior art retainers may tend to inhibit at least to some extent fluid flow around the retainer and in particular inhibit fluid flow space between the races and around all sides of the balls.
In view of the foregoing, it would be desirable to have a bearing assembly and method including a bearing retainer that alleviates the above mentioned problems at least to some extent. Further, it would be desirable to have a bearing retainer that provides desirable bearing retainment and/or spacing qualities while also operating in a dry running application. Further, it would be desirable to have a bearing assembly that facilities flow of cleaning or rinsing solution around the retainer itself and the balls.